Police were called to a house on Harwich Road at around 3.10pm on Thursday to deal with the incident.

The injured boy is still in hospital, while his mother was released after treatment for minor injuries, officers said.

A post-mortem examination on the body of the four-month-old boy is expected to take place next week.

Police said the dog, which is believed to have been a Staffordshire bull terrier-type, had been put down with the consent of its owner.

A post-mortem examination was due to take place on the animal yesterday.

Chief Inspector Elliott Judge said: "This is a tragic incident in which a young child has lost his life. We can confirm the incident took place inside a house on Harwich Road. The dog has been destroyed and no one has been arrested.

"An investigation to establish the facts surrounding what happened is ongoing.

"This is obviously a very difficult time for the family, who are being supported by specially trained officers."

Neighbour Scott Mills (24), who lives opposite the address, became aware of a "commotion" when he saw four police cars and two ambulances arrive at the family home.

He was among a crowd of concerned neighbours and passers-by who gathered as emergency services cordoned off the road. "When we heard that a baby had died, everyone was very upset - it's dreadful and so tragic," he said.

"There were a lot of children about because of the time - a lot of children were coming home from school."

Another neighbour, who did not wish to be named but was at home at the time of the incident, added: "The whole community is in shock. It's all very upsetting. You are caught off guard with these things.

"I am very upset about it all. My children saw it (the aftermath) and are very upset."

There have been 83 deaths from dog bites in England and Wales in the past 35 years.